The retrieval of cloud particle effective radius(re)from satellite remote sensing is a critical technique for studying cloud microphysical properties and precipitation processes.It has significant applications in aerosol-cloud interactions,severe convective weather monitoring and early warning,and weather modification.Accuracy validation of the retrieved re is essential for these applications. Based on improved satellite retrieval algorithm for cloud particle effective radius using 3.7 μm channel data,this study derives cloud particle effective radius(re_o)from MODIS and AVHRR observations.The retrieved re_o are systematically compared with in-situ re measurements by aircraft from 22 cases of continental cumulus cloud,and the algorithm's reliability and accuracy is evaluated. The comparisons show that the error of particle effective radius between the retrieval and airborne measurements is less than 2.4 μm,which is very close to 2 μm of international verification results within marine stratus.The distribution of re with temperature/height(vertical structure)is quite consistent with that detected by aircraft measurement.The retrieved re from the 3.7 μm has a high correlation with the airborne measurement,with a correlation coefficient of 0.79 and a linear fitting slope of 0.81.However,the re from MODIS cloud product has a low correlation with the airborne measurement,and the correlation coefficient and linear fitting slope are 0.43 and 0.32,respectively.All these results suggest high accuracy of the retrieved particle effective radius of clouds and the high reliability of the retrieved methodologies which demonstrate that improved algorithm can provide a reliable data foundation for applications.

Cold clouds are the main operation target of artificial precipitation enhancement, and its key is to find a supercooled cloud water area where the catalyst can be seeded to promote the formation of precipitation particles and increase precipitation to the ground. Based on the multi-spectral characteristics of the Fengyun-4A (FY-4A) satellite, a methodology for identifying supercooled cloud water is developed. Superimposed by a cloud top brightness temperature of 10.8 µm, a combination of 0.46 µm, 1.6 µm, and 2.2 µm red–green–blue (RGB) composites are used to identify the cloud phase and to obtain the real-time supercooled cloud water distribution every 5 min and in a 2 km resolution for the whole coverage of China. Based on the RGB composition, the supervised machine learning method K-mean clustering was applied to classify the cloud top phase. The results were validated extensively with Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP). It is worthwhile to highlight that the corresponding hit rate reached 87% over the full disk domain for both the summer and winter seasons. Furthermore, on 29 November 2019, microphysical properties were measured, and the data of supercooled cloud droplets and ice crystals were obtained using YUN-12 transport aircraft in Taiyuan. After simultaneously matching the satellite with an airborne track, the cloud particle image data were obtained near the cloud top and within the clouds during the climb and descending stages of the flight. The phase obtained from the microphysical properties of supercooled cloud droplets and ice crystals was compared with cloud phase results identified by FY-4A and Moderate Resolution Imaging Spectroradiometer (MODIS) cloud phase products. The case study and comparison show that (1) the supercooled water clouds and ice particles identified by FY-4A are in good agreement with those from the airborne measurement at the cloud top and within the cloud and (2) the positions and shapes of water clouds and ice clouds identified by FY-4A correspond well with MODIS cloud phase products. However, there is a small deviation in the extent of ice clouds, which is mainly located in the transition area between ice clouds and water clouds. The extent of ice clouds identified by FY-4A is slightly larger than that of MODIS products. Combined with airborne detection, the comparison shows that the ice clouds identified by the FY-4A satellite are consistent with aircraft detection. The supercooled cloud water identified by FY-4A can meet the needs of the operational precipitation enhancement of cold clouds, improve operational effectiveness, and promote the application of satellite technology for weather modification.

Bashan Mountain is the division line between middle subtropical climate and northern subtropical climate in China.The further analysis and understanding of the vertical variation of near surface temperature under such complex terrain can provide foundation and basic data for climate change， ecological monitoring and ecological environment protection in this region.Based on the measured data of daily near surface temperature on the northern slope of Micang Mountain during 2013 -2019 from four automatic stations and 3 surrounding meteorological stations， which covers an elevation difference more than 1400 m， combined the sounding data at Hanzhong sounding station from 2017 to 2019， the lapse rates （γ） of near surface temperature and ambient atmospheric temperature were compared， and the vertical variation of near surface temperature on the north slope of Micang Mountain was analyzed， also its vertical climate zone is discussed.The results show that： （1） The near surface temperature decreases with the increasing altitude， its monthly average temperature reaches the highest and lowest in mid-July and January respectively.The average annual γ is 0.624±0.136 ℃·（100m）-1 during the observation period， close to that of free atmosphere.The average monthly γ is the smallest in December， increases gradually to August and then decreases， representing a distinct seasonal trend that steeper lapse rates occurred during warmer months， while shallower lapse rates occurred during colder months.The seasonal γ are 0.647±0.099， 0.732±0.103， 0.605± 0.113 and 0.508 ±0.120 ℃·（100m）-1 in the spring， summer， autumn and winter， respectively.The variation of maximum/minimum temperature is similar with that of average temperature， with an annual γ 0.646±0.185 and 0.606±0.166 ℃·（100m）-1 respectively.The average annual daily range has no obvious difference in each height， fluctuating between 7 ℃ and 10℃， and has no obvious linear relationship with the height.The annual range decreases linearly with the increasing height.（2） The decreasing trend of γ has changed since 2008， which has largely contributed to the narrowing of the radiation difference at areas between higher and lower， and the opposite vertical change trend of aerosols.（3） With the increase of height， the accumulated temperature of daily average temperature passed 0， 5 and 10 ℃ decreases linearly， and their γ is almost about 213 ℃·（100m）-1， their initial day delays and the final day advances， and the duration shortens， and decreases by 3.4， 6.1 and 7.0 d·（100m）-1， respectively.（4） The hierarchy of ambient air temperature changes with height is different clearly among 0.5~1.0 km， 1.0~2.5 km， 2.5~4.5 km and 4.5 km above， in where their temporal variation of air temperature γ is also significantly different， reflecting the comprehensively topographical impact of Qinghai-Xizang Plateau， Qinling Mountain， local Micang Mountain and surface on air temperature.The γ of monthly air temperature near the surface is slightly greater than that of ambient air temperature， which is similar with that of 0.5~1.0 km after May.（5） The vertical climate zone can be divided into northern subtropical zone， warm temperate zone and middle temperate zone， which are between 500~1000 meters， 1000~1500 meters and 1500~2500 meters respectively.

Based on field observation from April 2017 to August 2020, the variations of aerosol scattering properties (σsp), PM2.5 mass concentration, scattering Ångström exponent (α) and meteorological parameters were investigated at a suburban station in Xian, northwest China. The annual mean value of σsp, PM2.5 and α during the observation period was 232.9±228.2 Mm-1, 58.6±57.1 μg/m3 and 2.76±0.36, respectively. The value of σsp and PM2.5 were all evidently higher in winter than in other seasons, which was mainly due to the unfavorable meteorological conditions and local emission of pollutants. The seasonal variation of α suggested that the anthropogenic fine particles was the predominance source of aerosol particles in Xian. Diurnal variations of σsp presented a bimodal pattern in spring and winter, a unimodal pattern in summer. And the mainly dominated parameters of the diurnal variation of σsp at Xian was the height of mix layer and the emission of human activities. The annual average of mass scattering efficiency was 5.9 m2/g in summer and about 1.5 times higher than that in other seasons. The σsp was remarkably higher under low wind speed especially in winter, which indicating that local pollutants attributed for the occurrence of haze pollution in Xian. High relative humidity was favored for the occurrence of low visibility weather at a certain σsp. The frequency of haze days was much higher in winter with high aerosol scattering coefficient. The mass scattering efficiency of PM2.5 was higher under light polluted condition, and increased from moderate to severe pollution episodes.

Operational cloud seeding has been implemented to alleviate local precipitation shortages in China for over half a century. Here, we present quantitative evidence for the effect of AgI seeding on supercooled layer clouds with a top cloud temperature of −15°C in China, as documented for the first time by a combination of radar, satellite, and disdrometer observations. A radar signature appeared 18 min after seeding, shortly followed by a visible glaciated seeding track. The seeding signature expanded horizontally at a rate of ∼1.4 and ∼0.3 m s −1 before and after 04:25 UTC. The radar signature descended to the surface 40 min after seeding. A disdrometer captured the precipitation of the first seeded raindrops that reached maximum diameter of 2.75 mm compared to the maximum diameter of 1 mm of the light background rain. The enhanced surface rainfall was observed within the subsequent 100 min. A conceptual model for the formation and expansion of the seeding track is presented. Although the precipitation was light, it is a promising step toward the goal of quantifying the impact of cloud seeding in China.

最近60多年,全球范围内广泛开展了人工增雨作业,但人工增雨效果检验一直是个难题.传统上,利用雨量计和目标/对比区统计数据评估人工增雨效果,结果大多不确定.对一次人工增雨作业而言,从科学上给出令人信服的效果检验更是没有好的解决方案.2017年3月19日,陕西省实施业务飞机冷云增雨作业播撒含有750 g碘化银(AgI)的催化剂,播撒线长125 km.作业后卫星、雷达观测到一条与播云线对应的清晰的云迹线,地面雨滴谱仪观测到相应的雨强、雨滴数浓度、雨滴直径增大,表明播云使云体产生了增雨响应.针对这次增雨过程,从连片雷达回波中分离增雨作用造成的回波增强带(增雨影响回波)和确定了自然降水回波强度,建立增雨影响回波强度(Z)与地面雨强(I)的拟合关系(Z-I关系),定量研究人工增雨的时、空演变.结果表明:(1)增雨影响时间约4 h,增雨影响回波区域(增雨影响区)面积为5448 km2.该区累计降雨总量和增雨总量分别为1.518×106 m3和8.04×105 m3,增雨影响区内增雨率达53％.(2)总降雨量、增雨量、自然降雨量随时间先增后减,总降雨量与增雨量的峰值同步,两者峰值都早于自然降雨峰值;催化后146 min(04时47分,世界时,下同),每6 min增雨量达到最大,为4.9×104 m3;催化后174 min(05时15分),增雨雷达回波面积达到最大(1711 km2),面积峰值滞后增雨量峰值出现.(3)增雨影响区位于播撒线下游,呈条带状;区域内总降雨量空间分布为中间大边缘小,与增雨量空间分布一致.(4)此次增雨作业改变了降雨时、空分布,促进降雨形成,增加了地面降雨量.

利用中国中纬度133个气象站夏季14:00(北京时)气候观测资料和2002-2018年MODIS夏季气溶胶光学厚度AOD(Aerosol Optical Depth)资料,把气候资料按气溶胶变化的转折年分为两个时间序列(建站至2011年,建站至2018年),通过对两个时间序列各站夏季风速、温度、海平面气压年变率和AOD的分布对比分析,研究了气溶胶对低层风速变化的影响.结果表明:(1)青藏高原(下称高原)地区夏季AOD较小,秦巴山区和平原地区AOD较大,2002-2011年AOD呈逐年增大趋势,而2002-2018年变为减小趋势,反映出我国2012年后环境治理成效.(2)2011年以前,高原和秦巴山区西部夏季以增温为主,而秦巴山区东部和内陆平原以降温为主,114°E附近降温最明显;与建站至2018年时间序列对比,在AOD减小的同时,降温和增压幅度都有所减小,反映出温度和气压变化对气溶胶的响应关系.(3)夏季风速普遍呈减小趋势,内陆平原减小幅度最大,年变率为-0.06～-0.02 m·s-1.结合气溶胶分析发现,风速年变率与AOD分布呈反位相关系.通过两个时间序列的对比,随AOD均值下降,对应风速减小程度有所缓解,反映了风速对气溶胶变化的敏感性.

准确反演气溶胶光学厚度(AOD)在气溶胶气候效应和环境效应研究中至关重要,仪器定标是目前AOD反演过程中最大的不确定性来源.Langley法作为应用最广泛的光度计定标方法,其对天气条件和大气洁净度要求苛刻,这在大气污染较重的地区难以实现,并可能导致AOD反演误差偏大.为了降低由不恰当的Langley定标所引起的AOD反演误差,本文提出一个利用辐射传输模式结合地面太阳直接辐射观测数据检验Langley定标结果合理性的方法,并利用西安2013年6月至2015年12月多滤波旋转遮光带辐射计(MFRSR)和直接辐射表(NIP)观测资料,探讨了方法的可行性.结果表明,该方法能够将Langley定标结果限定在较小的波动范围内,有效降低由定标不确定性引起的AOD反演误差,有助于提高单站点AOD观测精度.

The Tibetan Plateau (TP) plays an important role in formation and development of the East Asian atmospheric circulation, climate variability, and disastrous weathers in China. Among the many topics on TP meteorology, it is critical to understand the microphysical characteristics of clouds over the TP; however, observations of the cloud micro-physics in this area are insufficient mainly due to sparse stations and limited cloud physical data. The Visible Infrared Imaging Radiometer Suite (VIIRS), onboard the Suomi National Polar-orbiting Partnership (SNPP) satellite, has an improved imaging spectroradiometer with 17 channels of 750-m moderate resolution and 5 channels of 375-m image resolution. The high-resolution instrument has an advantage for observing the small or initial convective clouds. Based on the methodologies that we proposed before for retrieving cloud microphysical properties from SNPP, an automated mapping software package named Automatic Mapping of Convective Clouds (AMCC) has been developed at the scale of satellite swath. The properties of convective clouds are retrieved by AMCC and their values are averaged over 0.33° × 0.33° grids based on the SNPP/VIIRS satellite data over the TP during the summers of 2013–17. The results show that: (1) the temperature of lifting condensation level (TLCL) at Naqu meteorological station and the cloud base temperature (Tb) retrieved from VIIRS are linearly correlated, with a correlation coefficient of 0.87 and standard deviation (STD) of 3.0°C; (2) convective clouds over the TP have the following macro- and micro-physical properties. First, the cloud base temperature (Tb) is about −5°C, the cloud base height above the ground (Hb) ranges between 1800 and 2200 m, and the cloud water content is low. Second, the cloud condensation nuclei concentration (NCCN) is between 200 and 400 mg−1 with 0.7% in maximum supersaturation (Smax); consequently, the condensation growth of water cloud droplet with less NCCN and higher Smax is fast. Third, because the precipitation initiation depth (D14) varies within 1500–2000 m and 500–1000 m at the Yarlung Zangbo River basin and southern Tibet, respectively, the clouds over these areas are more prone to precipitation. Fourth, mean height of the cloud top above sea level (Htop) is between 10 and 13 km, but the cloud depth (Dcld) is rather small, which is about 5000 m in southern TP and gradually reduces to 2500 m in northern TP. Fifth, the glaciation temperature (Tg) ranges from −30°C in central and southern TP to −25°C in northern TP, which, combined with the warmer Tg and the Tb less than 0°C, leads to the domination of ice process in the clouds; (3) the macro- and microphysical properties of convective clouds over the TP explain why rainfall there is frequent and lasts over a short time with small amount and large rain drops.

The advent of the Visible Infrared Imager Radiometer Suite (VIIRS) on board the Suomi NPP (SNPP) satellite made it possible to retrieve a new class of convective cloud properties and the aerosols that they ingest. An automated mapping system of retrieval of some properties of convective cloud fields over large areas at the scale of satellite coverage was developed and is presented here. The system is named Automated Mapping of Convective Clouds (AMCC). The input is level-1 VIIRS data and meteorological gridded data. AMCC identifies the cloudy pixels of convective elements; retrieves for each pixel its temperature T and cloud drop effective radius r(e); calculates cloud-base temperature T-b based on the warmest cloudy pixels; calculates cloud-base height H-b and pressure P-b based on T-b and meteorological data; calculates cloud-base updraft W-b based on H-b; calculates cloud-base adiabatic cloud drop concentrations N-d,N-a based on the T-r(e) relationship, T-b, and P-b; calculates cloud-base maximum vapor supersaturation S based on N-d,N-a and W-b; and defines N-d,N-a/1.3 as the cloud condensation nuclei (CCN) concentration N-CCN at that S. The results are gridded 36 km x 36 km data points at nadir, which are sufficiently large to capture the properties of a field of convective clouds and also sufficiently small to capture aerosol and dynamic perturbations at this scale, such as urban and land-use features. The results of AMCC are instrumental in observing spatial covariability in clouds and CCN properties and for obtaining insights from such observations for natural and man-made causes. AMCC-generated maps are also useful for applications from numerical weather forecasting to climate models.

利用FY-2G静止卫星资料,采用多光谱综合分析方法,对2016年6月23日江苏盐城特大龙卷强对流灾害天气进行分析,重点分析强对流云微物理特征和识别强对流的卫星信号,并与雷达、TRMM卫星观测资料进行了对比分析.结果表明:(1)静止卫星RGB合成图能够可视化、便捷显示云微物理特征与发展趋势,对流云2区云团是产生龙卷的主云团,云系移动缓慢、位置基本保持不变是本次龙卷的特点,致使龙卷始终维持在盐城.(2)归纳出龙卷强对流云微物理特征和卫星信号为云顶高、云顶温度(Ttop)达到-80℃,存在过顶现象;云顶粒子有效半径(Retop)小、以小冰粒子为主,云砧结构明显,上部存在云粒子有效半径(Re)随温度(T)递减带;晶化温度(Tg)冷,达到同质冻结温度,对应有效半径(Reg)小.08:00(北京时)FY-2G已探测到l、2、4区云团具有强对流发展潜势,通过卫星跟踪云团强弱变化,及时发现灾害性强对流天气发生云团,加强对该云团监测,提前预警强对流灾害性天气发生,为静止卫星应用于强对流天气监测预警提供新途径.

青藏高原(下称高原)对东亚大气环流、气候变化及下游灾害性天气形成、发展有重要影响,研究青藏高原云微物理特征有重要意义.但因高原台站稀少,对云微物理研究不充分.NPP (National Polar-orbiting Partnership)卫星VIIRS(Visible Infrared Imaging Radiometer Suite)传感器包含17个中分辨率通道(750m)和5个高分辨通道(375m),具有反演初生小块对流云的优势,能够利用NPP/VIIRS反演对流云的微物理特征.利用NPP/VIIRS卫星格点对流云云物理自动反演(Automatic Mapping of Convective Clouds,AMCC)软件对高原地区2013-2017年夏季(6-8月)过境的VIIRS资料进行了反演,得到了高原对流云的宏、微观物理特征,并计算了这些物理量在0.33°×0.33°格点上的平均值.分析得出如下结论:(1)反演云底温度(Tb)与那曲探空计算抬升凝结温度(TLcL)线性相关,相关系数为0.87,均方根误差为3.0℃.(2)高原对流云宏、微观物理特征为:一是云底冷(Tb为-5℃),云底离地高度为1800-2200m,云内含水量低;二是云底云凝结核数浓度(NccN)为200-400个/mg,最大过饱和度(Smax)为0.7％,NccN少,Smax大,云滴凝结增长速率更快;三是降水启动厚度(D14)小,为1500-2000m,雅鲁藏布江流域及藏南地区D14约500-1000m,更加容易形成降水;四是云顶海拔高度为10-13 km,云厚度从南部5000m逐渐减小到北部2500m,云厚有限;五是晶化温度高,从中部、南部-30℃到北部-25℃,加之高原Tb＜0℃,使得云内降水粒子以冰相为主.(3)高原对流云的这些微物理特征决定了其降水具有多发、短时、量小、滴大的特点.这些结论进一步深化了对高原夏季对流云的科学认识.

The formation of new atmospheric aerosol particles and their subsequent growth have been observed under different environmental conditions globally; such observations are few over northwest China. Here, we present an analysis of some case studies for new particle formation (NPF) events from two distinct suburban locations in northern China during May and June of two consecutive years, and provide more information to understand the characteristics of NPF events in North China. Particle number size distribution was measured at suburbs of Beijing (39.75° N, 116.96° E) during 1 June to 2 July 2013 and at suburbs of Xi’an (34.09° N, 108.55° E) during 1 to 25 May 2014. The average of total particle number concentration in the similar size range of 10–487 nm at the suburbs of Beijing (9.0 × 103 cm−3) was about two times higher than those observed at Xi’an (4.7 × 103 cm−3), and the mean particle mode diameter at Beijing was 1.4-fold higher than that at Xi’an. The estimated total condensation sink (CS) at Beijing (3.11 × 10−2 s−1) was also higher than at Xi’an (1.13 × 10−2 s−1). The frequency of NPF events at suburb of Beijing was 24%, lower than that in Xi’an (50%), and also lower than urban site of Beijing (35% in June) and another suburb of Beijing (over 50% in June). The NPF events with (Class I) or without (Class II) subsequent growth were both observed at the two suburb sites. The derived GR at the suburb of Beijing (range from 4.6 to 8.6 nm h−1) was a little higher than that at Xi’an (range from 3.3 to 6.7 nm h−1), which are generally comparable to typical values in mid-latitude reported in previous studies. The air masses coming from north or northwest China favor the occurrence of NPF event under low condensation sink and clear days. The number size distributions of freshly nucleated particles showed clear bimodal distributions on both sites. Additionally, Mode Dp of nucleated particles at the two sites was 17 ± 1 nm and 22 ± 4 nm, respectively during the periods with NPF events. The case study of NPF events at the two suburb sites shows that the surface area concentration and total scattering coefficient (SC) was significant decreased during the NPF events at both sites. High temperature, low condensation sink and low relative humidity furthered the occurrence of NPF events, and wind direction shifts were important for the subsequent growth of particles. NPF events in the suburbs of Beijing usually occurred when relative humidity (RH) < 55%, CS < 0.02 s−1, or 55% < RH < 68%, CS < 0.01 s−1. However, there is no clear range for Xi’an. Furthermore, we observed that some NPF events occurred at higher RH and very low CS in this study on both sites, which means that low CS may be more important than low RH for the particle formation on clear days.

Interactions between absorbing aerosols and the planetary boundary layer (PBL) play an important role in affecting air pollution near the surface. In this study, a unique feature of the aerosol–PBL interaction is identified that has important implications in monitoring and combating air pollution. Opposite trends in aerosol loading between the lower and upper PBL are shown on a wide range of timescales and data acquired by various platforms: from a short-term field experiment to decadal satellite observations and multidecadal ground observations in China. A novel method is proposed to obtain the vertical profiles of aerosol loading from passive sensors by virtue of varying elevations. The analyses of visibility, aerosol optical depth, and extinction with different temporal scales exhibit the similar trend, i.e., increasing in the lower atmosphere but decreasing in the upper atmosphere. Integration of the reversal aerosol trend below and above the PBL resulted in a much less change in the column-integrated quantities. The surface cooling effect, together with the change in the heating rate induced by the absorbing aerosol, unevenly modifies the atmospheric temperature profile, causing a more stable atmosphere inside the PBL but a destabilized atmosphere above the PBL. Such a change in the atmospheric stability favors the accumulation of pollutants near the surface and the vertical diffusion of aerosol particles in the upper atmosphere, both of which are consistent with the observed reversal aerosol trends. These findings have multiple implications in understanding and combating air pollution, especially in many developing countries with high emissions of light-absorbing aerosols.

Particle number concentration and size distribution are important for better understanding the characteristics of aerosols. However, their measurements are scarce in western China. Based on the first measurement of particle number size distribution (10-487 nm) in the suburb of Xi'an, northwest China from November 2013 to December 2014, the seasonal, monthly and diurnal average particle number concentrations were investigated, and the characteristics of new particle formation (NPF) events and their dependencies on meteorological parameters also discussed. The results showed that the annual average particle number concentrations in the nucleation (N-Nuc), Aitken (N-AIT), and Accumulation (N-Acc) size ranges were 960 cm 3, 4457 cm 3, 3548 cm 3, respectively. The mean total particle number concentration (N-TOT) was 8965 cm(-3) and largely dominated by particles in Aitken mode. The number concentration was dominated by particles around 67.3 nm in spring, summer and fall, while about 89.8 nm in winter. The percentage of the ultrafine size range (UFP, particles of diameter below 100 nm) to total particle number concentration was 63.2%, 69.6%, 62.2% and 58.1% in four seasons. The diurnal variation of the nucleation mode particles was mainly influenced by NPF events in summer, while by both traffic densities and NPF events in spring, fall and winter. The diurnal variation of the number concentration of Aitken mode particles correlated with the traffic emission in spring, fall and winter, while in summer it more correlated with contribution of the growth of the nucleation mode particles. The burst of nucleation mode particles typically started in the daytime (08:15-16:05, LST). The growth rates of nucleated particles ranged from 2.8 to 10.7 nm ha with an average of 5.0 +/- 1.9 nm h(-1)Among observed 66 NPF events from 347 effective measurement days, 85 percent of their air masses came from north or northwest China, resulting in a low concentration of pre-existing particles, and only 15 percent came southerly from Qingling Mountains. Based on their growth rate, 64 and 36 percent of their subsequent particles, corresponding to types 1 and 2 NPF events, grew and seldom grew after the burst of nucleation mode particles. For type 1 NPF event, the nucleated particles could grow up to 40 nm or larger when surface winds shifted from westerly to easterly or southeasterly (from village areas). For type 2 NPF events, the particles kept almost unchanged when the winds stayed westerly. This implied that the surface wind direction with different emissions might play an important role in new particle growth in suburb of Xi'an. (C) 2017 Elsevier Ltd. All rights reserved.

为了进一步了解复杂的对流云冰相过程和气溶胶的成冰作用,利用多源卫星反演得到深厚对流云晶化温度(Tg)和-5℃有效半径(re-5),结合气溶胶分类和光学厚度,通过中国及周边141个个例统计分析结果表明:(1)污染气溶胶与沙尘具有相当成冰能力,当rre-5＜ 12 μm时,随气溶胶光学厚度的增加Tg变暖,成冰能力增强;(2)当re-5≥12 μm时,气溶胶使滴径减小,减弱冰晶繁生作用,从而降低云成冰能力;(3)对洁净海洋对流云而言,冰晶繁生机制为主要成冰机制,而大陆性对流云繁生作用仅占20％.

VIIRS (Visible Infrared Imaging Radiometer Suite), onboard the Suomi NPP (National Polar-orbiting Partnership) satellite, has an improved resolution of 750 m with respect to the 1000 m of the Moderate Resolution Imaging Spectroradiometer for the channels that allow retrieving cloud microphysical parameters such as cloud drop effective radius (re). VIIRS also has an imager with five channels of double resolution of 375 m, which was not designed for retrieving cloud products. A methodology for a high-resolution retrieval of re and microphysical presentation of the cloud field based on the VIIRS imager was developed and evaluated with respect to MODIS in this study. The tripled microphysical resolution with respect to MODIS allows obtaining new insights for cloud–aerosol interactions, especially at the smallest cloud scales, because the VIIRS imager can resolve the small convective elements that are sub-pixel for MODIS cloud products. Examples are given for new insights into ship tracks in marine stratocumulus, pollution tracks from point and diffused sources in stratocumulus and cumulus clouds over land, deep tropical convection in pristine air mass over ocean and land, tropical clouds that develop in smoke from forest fires and in heavy pollution haze over densely populated regions in southeastern Asia, and for pyro-cumulonimbus clouds. It is found that the VIIRS imager provides more robust physical interpretation and refined information for cloud and aerosol microphysics as compared to MODIS, especially in the initial stage of cloud formation. VIIRS is found to identify significantly more fully cloudy pixels when small boundary layer convective elements are present. This, in turn, allows for a better quantification of cloud–aerosol interactions and impacts on precipitation-forming processes.

The advent of the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-Orbiting Partnership (NPP) satellite provided a quantum jump in the satellite capabilities of retrieving cloud properties, because it nearly tripled the resolution in the thermal channels (375m). This allowed us to develop a methodology for retrieving convective cloud base temperature (T-b) and validate it over the Atmospheric System Research Southern Great Plains site for the satellite early afternoon overpass time. The standard error of the T-b retrieval was only 1.1 degrees C. The knowledge of T-b allows the calculation of cloud base height and the depth of the boundary layer, as well as the boundary layer water vapor mixing ratio with an accuracy of about 10%. The feasibility of retrieving cloud base temperature and height is an essential component that is required for retrieving cloud condensation nuclei (CCN) from satellites by using convective clouds as natural CCN chambers.Key Points Convective cloud base temperature was retrieved from satellite with 1 degrees C accuracy Boundary layer vapor mixing ratio was retrieved with 10% accuracy This became possible by using the 375 m resolution of the NPP/VIIRS Imager

通过卫星多光谱资料的定标,利用可见光反射率、3.7μm和11μm辐射亮温,反演了云顶粒子有效半径、云顶温度等云特征参数。运用图像合成技术,建立了反映云宏、微观特征的RGB合成图。利用发展的多光谱云微物理综合分析方法,通过极轨卫星分析了不同过冷层状云及其降水特征,结合增雨假设,总结出适宜人工增雨作业的卫星判据为：云厚大于1.5km,云顶温度-5～-15℃时,有效半径小于25μm;或云顶温度-15～-25℃时,有效半径小于15μm。利用可见光反射率、云顶温度和有效半径多阈值建立人工增雨播云等级和分级显示。通过静止卫星跟踪云系演变,进一步确定播云部位和作业时机,指导人工增雨作业。

The temporal and spatial variations and causes of aerosol optical depth (AOD) in Shaanxi Province were investigated based on the Moderate Resolution Imaging Spectroradiometer (MODIS) derived aerosol data for the period of March 2000–February 2012. The results showed that the distribution of aerosol was largely affected by topography and local economic activities. Heavy aerosol loading and increasing tendency in AOD was observed in Guanzhong, Hanzhong and Ankang basin, while a reverse tendency was revealed in most other regions. The spatial distribution of aerosol Angstrom wavelength exponent was predominantly related to vegetation coverage in Shaanxi. Airborne dust from ground is an important source of coarse mode aerosols. Vegetation improvement indicated by an increase in normalized difference vegetation index (NDVI) and a reduction in dust weather led to a gradual decrease in coarse mode AOD to the north of Qinling Mountains in Shaanxi, while anthropogenic activities led to an increase in fine mode AOD in other areas except those covered by forests. The main aerosol type gradually shifted to the urban industrial type in Shaanxi.